How do you change the colors of 2 objects with nodes?
Since the OP said that this is what helped, then the answer to this question is to use material nodes, not the compositor nodes for the purpose of changing material properties with context sensitivity being per selection in the 3D viewport.

Albeit, the compositor nodes can definitely be used to change visual properties of everything (with a high degree of power and with a great myriad of approaches), in this case I believe that my prior statement is the answer for this question.

For whatever the reason may be (newness to the software, lack of experience in node editing, etc...), I imagine it to be true that this particular question would be very hard for a user at a beginning level of understanding to articulate.  This being said, I hope that this helps somebody else who may be searching for the same/similar solution in the future gain good information; even though it may be hard for them to describe.